1. Field of the Invention
The present invention relates to an adjustable suspension device and, more particularly, to an adjustable magneto-rheological fluid device that changes vibration damping and suspension characteristics by controlling the flow of a magneto-rheological fluid through a flexible magneto-rheological fluid compartment to influence the flow of a hydraulic fluid to control the movement of a piston.
2. Background Information
Devices using fluids with controllable characteristics for suspending parts and damping their relative movement are well known. These devices are typically used in vehicle suspension systems and employ electro-rheological (ER) fluids or magneto-rheological (MR) fluids. Designers are more frequently turning to MR fluids, however, due to advantages over ER fluids in yield shear strength (up to 150 kPa versus 20 kPa), power requirements (5 to 12 V versus 20 to 30 kV) and sensitivity to chemical and particulate contamination.
Presently known devices typically include a piston disposed within a cylinder that is filled with a controllable fluid. One end of the cylinder is fixed to one moving part, while a piston rod attached to the piston extends from the opposite end of the cylinder and is fixed to the other moving part. There is a restricted passage, either within the cylinder or within the piston, that is activated to electrically or magnetically control the characteristics of the controllable fluid. The relative movement of the parts is regulated by controlling the characteristics of the fluid which in turn controls the movement of the piston within the cylinder.
The very feature that makes these devices advantageous (the controllable fluid) also makes these devices susceptible to reliability problems due to the abrasive nature of the controllable fluid. The particles suspended in the fluid, which give the fluid the ability to change characteristics upon application of an electrical current or magnetic field, are constantly in abrasive contact with the seal between the piston and the cylinder, breaking the seal down. This leads to a loss of precision in controlling the device as the fluid is allowed to escape around the piston.
In order to address this abrasion problem, special seals and piston components can be used. Their use, however, does not entirely solve the problem. Additionally, these special seals and components disadvantageously increase the cost of the device.
Further, controllable fluids used in the present known devices must have a low volatility and be carefully monitored as movement of the sliding surfaces causes friction that generates heat. The volatility of the controllable fluids used must be low enough that the generated heat does not cause flashing.
Additionally, many known devices have fixed properties that cannot adapt to a changing load. Changes in the suspended mass or movement of an associated vehicle change the load compensation of the device. Devices having fixed suspension elements are not able to adequately respond to these changes in the suspended mass. Thus, without real time compensation for changes in the suspended mass, these devices do not compensate for changes in the suspension natural frequency, leading to less than desirable performance.
Also, these many known devices undergo significant temperature increases during operation. This increasing temperature affects the gas-filled chambers, thus changing the suspension characteristics of the device.
Finally, utilization of the presently-known single cylinder devices is limited by the length of the device. In these devices, all of the components are aligned linearly, wherein applications with small space requirements are left unsatisfied.
It is therefore an object of the present invention to eliminate the abrasion between the controllable fluid and the sliding surfaces of the device. A further object of the present invention is to overcome the aforementioned drawbacks of the prior art. Another object of the invention is to automatically adjust the suspension characteristics of the device to compensate for changes in the suspended mass and the suspension natural frequency. A further object is to compensate for changes in the temperature of the device that affect the performance characteristics of the device.